Search Results

Sort by

Electrodynamic shakers or exciters are commonly used in experimental modal analysis. The practical aspects regarding the setup of the shakers, stingers and transducers are often the source of test difficulties and avoidable measurement errors. This paper reviews the basics of shakers as beneficial to modal testing, and common problems associated with setup issues and resulting measurement errors. These include shaker alignment, sensor's considerations, stinger selection, amplifiers, reciprocity assumptions and other test related circumstances.

It is very important to accurately measure rotation frequencies and fluctuations of rotating systems since they cause vibrations and noises, and since they sometimes indicate system malfunctions. Most rotating systems are equipped with electro- or magneto-conductive gears as their components, and rotation pulses are very commonly obtained by installing electromagnetic or electrostatic type sensors closely to target gears, and time dependent (instantaneous) rotation frequencies are obtained from intervals between adjacent pulses. However, since the number of pulses per revolution is relatively small, a method of obtaining instantaneous frequencies from adjacent pulse intervals is not adequate. For these kinds of pulses, instantaneous rotation frequencies are typically derived using the analytic signal (or Hilbert transform) method. In either case, there is an inherent limitation in using rotation pulses obtained from gears.

Research into the estimation of diesel engine combustion metrics via non-intrusive means, typically referred to as “remote combustion sensing” has become an increasingly active area of combustion research. Success in accurately estimating combustion metrics with low-cost non-intrusive transducers has been proven and documented by multiple sources on small scale diesel engines (2-4 cylinders, maximum outputs of 67 Kw, 210 N-m). This paper investigates the application of remote combustion sensing technology to a larger displacement inline 6-cylinder diesel with substantially higher power output (280 kW, 1645 N-m) than previously explored. An in-depth frequency analysis has been performed with the goal of optimizing the estimated combustion signature which has been computed based upon the direct relationship between the combustion event measured via a pressure transducer, and block vibration measured via accelerometers.

Highly effective double-wall systems for automotive applications can often have over a 90 dB span in sound transmission loss values between low frequencies, where they are usually least effective and upper frequencies, where they are typically most effective. Particularly for 16-bit measurement systems, but even for 24-bit systems, this can represent a very difficult scenario for measurements in either the source and/or receiving chamber(s). A methodology to balance the observed dynamic ranges in both source and receiving chambers is presented and discussed in this paper. An improved sound transmission loss measurement system can therefore be implemented which reduces the potential of overload or noise floor contamination occurring in measurements within either chamber. Low frequency SPL requirements for the source chamber speaker system and flanking noise issues with adjacent test chambers can also be typically reduced.

Gulfstream Aerospace Corporation (GAC) owns and operates an Acoustic Test Facility (ATF) in Savannah, GA. The ATF consists of a Reverberation Chamber, Hemi-Anechoic Chamber, and a Control Room. Types of testing conducted in the ATF include Transmission Loss, Sound Power, and Vibration testing. In addition to accommodating typical types of acoustic testing, the ATF has some unique capabilities. The ATF can be used to conduct testing at cold temperatures representative of up to 45,000 ft flight altitude, while simultaneously taking Transmission Loss measurements of the chilled test sample. Additionally, the ATF has the capability of conducting Transmission Loss testing of a full mockup of the aircraft sidewall, including a section of fuselage, all the thermal/acoustic materials up to and including the interior decorative panel. A sound source capable of very high amplitudes at high frequencies is required to obtain good measurements from testing multiple wall systems such as this.

A cold turbocharger test facility was designed and developed at The Ohio State University to measure the performance characteristics under steady state operating conditions, investigate unsteady surge, and acquire acoustic data. A specific turbocharger is used for a thermodynamic analysis to determine the capabilities and limitations of the facility, as well as for the design and construction of the screw compressor, flow control, oil, and compression systems. Two different compression system geometries were incorporated. One system allows compressor performance measurements left of the surge line, while the other incorporates a variable-volume plenum. At the full plenum volume and a specific impeller tip speed, the temporal variation of the compressor inlet and outlet and the plenum pressures as well as the turbocharger speed is presented for stable, mild surge, and deep surge operating points.

Test Facilities for Vibrations and Acoustics can be very complicated. With the addition of necessary high power motor dynamometers for load application, the complexity of the test cell increases dramatically. The motors and subsequent additional fixtures and shafts necessary to apply loading conditions can produce additional source noises that would interfere with test measurements. In addition, facility interfaces can dramatically influence the test cell setup and reduce the measurement capabilities. This paper addresses common considerations needed in considering a new test cell for driveline vibration, acoustics, efficiency, and durability testing using motored dynamometers. In addition to outlining common design points, a practical application of 2 new dynamometers utilized for vibration, acoustics, efficiency, and durability testing and their subsequent capabilities are outlined.

Previously part of a larger OEM, Spirit AeroSystems became a standalone company 5 years ago and is currently a Tier One supplier of aerostructures. Products include fuselage components, wing structures, engine struts and nacelles, and at the request of various OEMs, fully stuffed fuselages and podded engines where all of the wiring, heating, duct work, etc. is installed prior to delivery. While operating as part of the Propulsion Structures and Systems Business Unit, the design, testing and analysis services provided by the acoustics lab potentially impact all programs at all stages of development because of increasing noise regulations and material certification requirements for implementation in high noise environments.

Many applications in acoustics, such as transfer path analysis and synthesis (the well-known tools for troubleshooting and sound design of vehicle interior or exterior noise), require the measurement of transfer functions. Several methods are available to determine the transfer functions between identified sources and selected receiver locations. For example, transfer functions can be obtained by means of direct or reciprocal measurements. Due to errors and restrictive constraints during the measurements, the results of the two methods differ. The quality of measured transfer functions must be evaluated with respect to the auralization of the synthesized receiver signals or even the auralization of individual noise shares caused by a specific source and transmitted via one or a combination of paths. This paper compares the different measurement techniques of transfer functions in theory and in practice.

Advanced engine test methods incorporate several different sensing and signal processing techniques for identifying and locating manufacturing or assembly defects of an engine. A successful engine test method therefore, requires advanced signal processing techniques. This paper introduces a novel signal processing technique to successfully detect a faulty internal combustion engine in a quantitative manner. Accelerometers are mounted on the cylinder head and lug surfaces while vibration signals are recorded during engine operation. Using the engine's cam angular position, the vibration signals are transformed from the time domain to the crank-angle domain. At the heart of the transformation lies interpolation. In this paper, linear, cubic spline and sinc interpolation methods are demonstrated for reconstructing vibration signals in the crank-angle domain.

A powered seat adjuster is a complex mass-produced assembly that is heavily optimized for low cost and light weight. The consequence is an inevitable degree of uncontrolled variation in components, subassemblies, and final product. Automakers are driving an exceptional focus on quality and the showroom experience of the car buyer is paramount. Therefore, any seat adjuster with the potential to not satisfy the customer's expectation is likely to be screened on the production line. This paper describes NVH metric design in the context of automated production line detection of seat adjuster defects. A key requirement of the production environment is that the metrics offer intuitive explanations of possible defects and are based on industry-standard formulations. The metric set is a hybrid of objective and subjective parameters with a focus on ensuring a robust sorting process that maximizes detection while minimizing the possibility of failing acceptable product.

Durability testing of engine mounted components is often performed using sine testing. To ensure that all resonance frequencies are excited, swept sine is used across the frequency range of excitation for the engine. This can be very costly and time consuming. A consortium of German automobile manufacturers recently approved the use of multiple simultaneous swept sine tones to reduce the time and cost of durability testing of engine mounted components. This paper describes a new multi frequency sine control technique that uses multiple swept sine control loops with independent digital tracking filters. The primary advantage of this technique is that it significantly reduces the required test duration. The result is a system capable of smooth continuous sine sweeps that excite all frequencies in the test range without sacrificing control performance.

Microphone arrays used in vehicle acoustics are mainly designed for fast setup and basic evaluation (e.g. using delay-and-sum beamforming) resulting in a restriction to free field environments. Applications in vehicle interiors require advanced source localization techniques taking into account the reflections at the different panels appearing as mirror sources. Coherence filtering techniques allow for the detection of these mirror sources. An additional sensor is placed as a reference close to the main source. This reference signal is used to filter the array signals increasing the overall dynamic range of the acoustic source mapping. The discrimination of the original source and the reflections is obtained by manipulating the impulse responses between the reference signal and all microphone signals.

The NVH (Noise Vibration Harshness) behavior of modern vehicles becomes more and more important - especially in terms of new powertrain concepts, like in hybrid electric or full electric vehicles. There are many tools and methods to develop and optimize the NVH behavior of modern vehicles. At the end of the development process, subjective ratings from road tests are very important. For objective analyses, different approaches based on artificial neural networks exist. One example is the AVL-DRIVE™ system, a driveability analysis and benchmarking system which allows, based on a very small set of sensors, an adequate objective rating of the vehicle's driveability. The system automatically detects driving maneuvers and rates the driveability. This article presents a method which is able not only to rate different maneuvers and the behavior of the vehicle but also to detect phenomena and causes in the domain of NVH.

Pass by noise is a complex test that requires meeting several different standards with regard to the physical track layout, measurement systems, data acquisition, triggering, processing and analysis. Overview of the pertinent standards for Tire and Vehicle pass by testing is provided along with the description of development of an advanced solution to meet our specific needs. Key features of the solution are provided along with the lessons learned from our operation of the system at our facility and several other test tracks.

When testing dynamic structures, it is important to note that the dynamic system in question may be submerged into a fluid during operation and to properly test the structure under the same condition in order to understand the true dynamic parameters of the system. In this way, the mass and stiffness coupling to the particular fluid, for the case of this study, automatic transmission fluid, may be taken into account. This is especially important in light structures where the coupling between the fluid mass and the structural mass may be great. A structure was tested with a laser vibrometer using several impact methods in open air to determine which impact method would be most suitable for submerged testing. The structure was then submerged in transmission fluid with an accelerometer attached and subsequently tested and compared to the previous results.

Several methods have been established to measure the normal incidence transmission loss of noise control materials using the standing wave tube. In the automotive NVH field, multi-layered systems are common-place, for example in the interaction between the traditional mass-decoupler dash insulator and the front dash sheet metal. Most of the sound transmission loss studies utilizing the standing wave tube have so far been focused on single layer systems with only a limited number of studies on multi-layered systems. Therefore there is only some degree of information on the correlation between this said method and the more widely accepted two-room methods of determining sound transmission properties in these systems.

As North American truck manufactures have entered the global market it has become apparent that there are widely varying drive-by noise regulations required in various areas of the world. This paper will describe differences between various test procedures, track layouts, and required levels. Data will be presented showing vehicle results from various procedures, used to quantify differences in noise levels between a range of procedures. Countries were ranked from least restrictive to most restrictive based on test procedures and legal market requirements.

An existing pass by noise data acquisition system was upgraded to provide the sophisticated data analysis techniques and test site efficiency required to comply with the current and future drive by noise regulations. Use of six sigma tool such as voice of the customer helped in defining the customer requirements which were then translated into the desired engineering characteristics using QFD. Pugh concept matrix narrowed down the best option suitable for the test site modifications taking into account the critical constraints such as test complexity, system cost & transparency to the existing drive by noise setup. Features of the new system include data telemetry, frequency analysis, portability and efficient data management through the use of advanced data acquisition system. Wireless mode of the data transmission helped significantly avoid most of the test site modifications, which in turn helped to reduce the overall system implementation cost.

In response to a growing need for a practical and technically valid method for measuring exhaust sound pressure levels (SPL) of on-highway motorcycles, the SAE Motorcycle Technical Steering Committee has developed Surface Vehicle Recommended Practice J28251, “Measurement of Exhaust Sound Pressure Levels of Stationary On-Highway Motorcycles,” which includes a new stationary sound test procedure and recommendations for limit values. Key goals of the development process included: minimal equipment requirements, ease of implementation by non-technical personnel, and consistency with the federal EPA requirements; in particular, vehicles compliant with the EPA requirements should not fail when assessed using J2825. Development of the recommended practice involved a comprehensive field study of 25 motorcycles and 76 different exhaust systems, ranging from relatively quiet OEM systems to unbaffled, aftermarket exhaust systems.